This invention relates generally to the field of producing lightweight cementitious compositions and products formed therefrom.
The methods of preparing lightweight cementitious materials, such as lightweight concrete, heretofore available have not been entirely satisfactory for the reason that all of the methods known to the inventor require the addition of various constituents to achieve a strong but lightweight concrete mass that has a high homogeneity of constituents and which is uniformly bonded throughout the mass. There have been several patents issued relating to lightweight concrete using expanded polystyrene beads and the like, but all of the previous methods simply added an amount of compressible aggregate to conventional concrete mixtures, and have usually utilized expandable polystyrene beads that are expanded by various heating methods either before the beads are introduced into the concrete mixture, or expanded after they have been added to the concrete mixture.
It has been necessary in the past to coat the polystyrene beads after they have been expanded with some type of bonding agent in order to uniformly disperse the lightweight beads when admixed into heavy cementitious material. An example of such a method is taught in U.S. Pat. No. 3,764,357 issued to Bowles and Parsons. This patent teaches the wetting of the surfaces of the lightweight aggregate particles with an aqueous medium and admixing the wet aggregate particles with dry, finely divided cementitious material to form a coating about the particles before adding the particles to the concrete mix. U.S. Pat. No. 3,869,295 issued to the same individuals teaches the preparation of expanded polystyrene beads by expanding same in hot water for the purpose of reportedly attaining increased strength.
U.S. Pat. No. 3,214,393 issued to Sefton teaches a light-weight concrete material that is comprised of cement, a primary aggregate, expanded styrene polymer, a specific homogenizing agent consisting of polyvinyl alcohol, a bituminous compound, and an alkali metal salt. Another prior art composition is found in U.S. Pat. No. 3,021,291 issued to Thiessen, which teaches a cellular concrete product that reportedly has superior resistance to impregnation by water and vapor. The Thiessen patent teaches a mixture containing a polymeric material which will expand under the influence of heat during the curing to sufficiently fill the voids in the concrete, the polymeric material having an expanding agent incorporated therein.